Patent GB-670003-A (GB)
Title: Improvements in or relating to process of producing glutamic acid and the glutamic acid resulting from said process
IPC: F02P3/04
Filed: 1948-11-29
Abstract: <PICT:0670003/IV (b)/1> Glutamic acid particularly that recoverable from concentrated Steffen's filtrate is crystallized by maintaining a circulating slurry stream of glutamic acid crystals and mother liquor at a pH between about 3.1 and 3.3 in a circuit containing a mixing zone and at least one hold-up (crystallizing) zone, adding to the mixing zone a solution of glutamic which has been prepared by hydrolysis of a protein capable of yielding glutamic acid on hydrolysis and which solution on adjustment to the said pH will crystallize out glutamic acid, and maintaining the said pH of the circulating slurry stream by adding to the mixing zone a mineral acid non-oxidizing under the conditions obtaining and withdrawing a portion of the circulating slurry stream.  The solution of glutamic acid added to the mixing zone may be obtained by hydrolysing concentrated Steffen's filtrate with caustic soda at an elevated temperature, quenching the hydrolysate, acidifying the quenched hydrolysate with hydrochloric acid to a pH between about 5 and 6, evaporating the acidified mixture to the point of crystallizing inorganic salts, and separating these salts to obtain the glutamic acid solution.  The process may be carried out batchwise, continuously or semi-continuously.  The non-oxidizing mineral acid is preferably hydrochloric acid but sulphuric and phosphoric acid may be used.  Also alkalis other than caustic soda, e.g. caustic potash and calcium hydroxide may be used in the recovery of the glutamic acid from concentrated Steffen's filtrate.  The glutamic acid is finally converted to monosodium glutamate by the conventional treatment with caustic soda.  In the Figure, concentrated Steffen's filtrate is filtered to remove organic salts and then concentrated in evaporator 8.  The concentrated product is then hydrolysed in vessel 16 with caustic soda or other alkaline solution at 80-95 DEG  C. and after cooling the hydrolysate is acidified with hydrochloric acid or other non-oxidizing mineral acid in tank 25 to a pH of between 5 and 6. The hydrolysate is then heated and passed to evaporator 32 where the liquid is evaporated to crystallize a substantial portion of the inorganic salts which are then filtered off in centrifuge 39. The filtrate is then passed into tank 44 into which hydrocloric acid is introduced by line 48 either directly into the tank via line 49 or first into a recycle stream by line 51.  The filtrate from centrifuge 39 is conducted directly into tank 44 by lines 41 and 42 or all or a portion of the filtrate in line 41 may be conducted into the recycle stream through line 61.  Sufficient acid is added through line 48 to give a pH of between 3.1 and 3.3. A circulating slurry of glutamic acid crystals and mother liquor is maintained in the tank 44 and is withdrawn into crystallizer 55 which may comprise a plurality of tanks connected in series and serves as a retention tank or hold-up zone or as a series of retention tanks or hold-up zones.  The slurry is withdrawn through line 58 and recycled to the mixing tank 44 via cooler 65 and line 53 thus establishing a circulating stream of crystallizing slurry.  This circulating slurry is maintained at a temperature of 25 DEG  to 40 DEG  C. and the ratio of recirculated slurry to solution feed should exceed 5 to 1 by volume. Previously produced small seed crystals of glutamic acid may be added to the system through line 78.  A constant volume of liquid is maintained in the system by withdrawing a volume of slurry equal to the total volume of liquid added.  The withdrawn slurry is passed into ageing crystallizer 57, which may comprise one or more tanks, in which the newly formed crystals build up into larger crystals by allowing them to stand for several days.  The slurry is then thickened in thickener 68 and the thick slurry effluent is filtered in centrifuge 85 to separate the larger crystals.  The overflow from the thickener is combined with the effluent from the centrifuge and passed through a polishing filter 71 and a portion or all of the resulting filter cake is slurried in tank 74 with a portion of the circulating slurry or with a purified glutamic acid filtrate and all or part of the resulting slurry is employed as the seed slurry introduced into the system through line 78.  The crude glutamic acid crystals from centrifuge 85 together with that portion of the slurry from the tank 74 which is not employed for make up slurry are then repulsed in tank 90 and the repulped material then centrifuged.  The centrifuged cake is then slurried with wash water and filtrate obtained after a final filtration from the subsequent purification of the glutamic acid and this slurry which has a pH of about 3.1 to 3.3 is then purified as follows (Fig. 2, not shown).  The crude glutamic acid slurry is mixed with a decolourizing agent, such as activated charcoal and some filter aid, caustic soda is added to give a pH of 5.7 to 6.0 and the mixture maintained at 50 DEG  to 65 DEG  C.  The mixture is then filtered and the filtrate introduced into a glutamic acid crystallizing tank and the same system may be employed for crystallizing this purified glutamic acid as is described above for the crystallization of the crude acid, hydrochloric acid being added to maintain a pH of 3.1 to 3.3.  The withdrawn slurry is preferably aged as before and the slurry is then centrifuged or filtered.  The filtrate from the centrifuge may be used in tank 74 (Fig. 1), for slurrying the seed crystals. The filter cake is washed and is then slurried with waste water from a subsequent washing of filter cake and this slurry is then treated with caustic soda in the presence of a decolourizing agent, such as activated carbon, and a filter aid, sufficient caustic soda being added to give a pH of about 7.  This treatment is effected at 50 DEG  to 55 DEG  C. for about 1 to 2 hours and the mixture is then filtered and washed with water the wash water being used for slurrying the above filter cake of purified glutamic acid.  The water white filtrate comprises an aqueous solution of monosodium glutamate and it is then mixed with non-marketed subsequently produced crystals of monosodium glutamate.  The solution is then subjected to several stages (preferably four) of alternate evaporation and crystallization with the filtrate or overflow from the centrifuge becoming, after each crystallization, the liquor evaporated in the next evaporation stage.  Four separate strikes of crystals may thus be recovered.  The last strike or the last two strikes of crystals may if desired be further purified by recycling them to the last described decolourizing treatment and the filtrate or overflow from the first two strikes together with wash water from the crystals may be introduced upon acidification with hydrochloric acid to a pH of 3.1 to 3.3 into the purified glutamic acid crystallization system.